Rubber plasticizers



, Patented Apr. '10, 1945 Russell T. Dean, Stamford, Conn.,, assignor to American Cyanamid Company, New York, N. Y., a corporation of Maine No Drawing. Application July 24, 1942,

Serial No. 452,203

Claims.

This invention relates to thetreatment of rubber and, more particularly, to theproduction of rubber compositions of increased .plasticity.

It is well known that when rubber is subjected to mechanical working in the presence of oxygen it is rendered more plastic. However, it is frequently desirable to accelerate this plasticization and thus shorten the-time of milling.

It is an object of the present invention to provide a process for increasing the rate of breakdown of unvulcanized rubber and for making it more plastic. It is a further object of this invention to provide an unvulcanized rubber of increased plasticity. It is an additional object to provide a new class of rubber plasticizing agents.

The foregoing and other objects may be at- The plasticizing agents will be more effective at elevated temperatures, e. g., above about 50 C. Any temperature at which rubber may be" heated without detrimental eflect may be used, e. g., up to about 150 C.

The invention is further illustrated by the following specific examples to-which, however, it is tained by, subjecting unvulcanized rubber to" the action of a small amount of a salt of a pseudourea by milling or similarly mixing unvulcanized rubber therewith for a short time at an elevated temperature. These salts may be represented by the following general formula:

in which, R' is an alkyl or an aralkyl radical arid HX is asaft-forming acid. The alkyl radical may be saturated or unsaturated, straight-chain, branched, or cyclic, and ,may be substituted by such groups as hydroxyl, alkoxy, nitro, halogen, or the like. The aralkyl radicals may also carry similar substitfient .groups.

As illustrative, the salts of the substituted pseudo-ureas may be prepared by the reaction of cy'anamide: cyanamide dihydrochloride and an appropriate alcohol. The procedurewhich may be'followed is typified by Example 1,of U. S. Pat- 'ent No. 2,156,193. By further reacting this condensation product in a suitable solvent with a sodium salt of a desired fatty acid, other salts of the pseudo-urea may be formed.

The most desirable point for the addition of I the plasticizing agent is just after preliminary milling of the rubber and preferably, in the absence of compounding ingredients, especially sulfur. i.

In general, the amount of plasticizing agent to be added will not be much above 1% of the weight ofthe rubber; for example, about 0.375%. Larger amounts may be-used if'desired but this is generally uneconomical since a proportionate increase in the plasticizingefiectis not obtained;

- The plastici'zing agent maybe used singly or in admixture with one or more other similar agents. as will be apparent to one skilled in the art.

not'to be limited. Unless otherwise stated, parts are given by weight. The softeni'ngeffect of the compounds on the rubber intheseexamples was determined in accordance with a modification of the well-known Zimmerman-and Cooper method (Industrial and Engineering Chemistry, 20, p. 812, 1928) The plasticity measurements were made in a"Wi1liams plastometer at 100 C. using a 3-minute. Y" value; The decrease in Y" value indicates the higher plasticity or softening of the rubber obtained by using the plasticizers set forth.

Example Four hundred and twenty parts of smoked sheet rubber were placed on 12-inch rolls, the initial temperature of the rolls being 95 C. After milling for live minutes, 20 parts of rubber (A) were removed for purposes of the test and to the remaining 400 parts of rubber on the mill were added 1.5 parts (0.375%) of the plasticizer compound. Milling of this rubber mix was continued for an additional five minutes to give the finished batch (B). The following tabulation indicates the increase of plasticity on the basis of "Y values for the several plasticizers indicated.

- Y values Compound Control (no plasticizer 0. 165 0. Cyclohexyl pseudo-urea stearate. 0.166 0.145 2-ethyl hexyl seudo'urea stearate.. 0. 174 0. 147 Isoamyl pscu o-urea stearate.... 0. 173 0. 153 n-Octyl pseudo-urea stearate. 0. 0. 146 Lauryl pseudo-urea stearate... 0. 0. 146

Compounding and vulcanization of the plasticized rubber may be carried out in a manner known to those skilled in the art. .Because of the reduction in time of mechanical working obtained in accordance with this invention, the rubber treated thereby',in general, will give vulcanized stocks with better physical properties. Mixtures of the plasticized rubber may be made with compatible synthetic rubber-like materials if desired.

My compounds may be utilized in rubber ce- '-ments by dissolvingln a solvent, unvulcanlzed rubber which has been plasticized with a softenhis agent of the present invention.

The activity of the compounds as plasticizers appears to be influenced by the substituent attached to the oxygen atom of the pseudo-urea nucleus. The preferred compounds are generally the higher fatty acid salts of the pseudo-ureas. The pseudoor isourea nucleus may be that of an of the following: n-butyl isourea. sec. butyl isourea, isobutyl isourea, amyl isourea, decyl iso-= urea, dodecyl isourea, benzyl isourea, cyclohexyl isourea, octadecyl isourea, he'xadecyl isourea, noctyl isourea. The acids used in the salts are usually the higher fatty acids but plasticizins compounds maybe obtained utilizing salts of any or the following acids: acetic, propionic, n-butyric, isobutyric, 2-ethyl butyric, Z-ethyl hexoic. lauric, palmitic, stearlc, phenyl acetic, p-toluene sulfonic, p=toluene sulflnic, benzoic, phthalic, succinic, naphthoic, sulfonic, phenyl benzoic, naphthyl benzoic, and halogen substituted acids such as the chloracetic acids.

Suitable variations and changes in the inven= tion may be made without departing from the spirit thereof or the scope oi the following claims, which are to be construed as broadly as is per- 'nissible in view of the prior art.

I claim:

1. A process of increasing the plasticity of rubber which comprises milling unvulcanized rubber in the presence of a small amount of a salt of a pseudo-urea, said salt being represented by the following general formula:

R--C==NH-HX in which R is a member of the class consisting of the cyclohexyl, benzyl and the alkyl radicals having from about 4 to 18 carbon atoms and HK is a higher fatty acid, for a time suiilcient to effect an increase in the plasticity of the rubber over that which it would have if subjected to the same conditions in the absence of said salt.

2. A process of increasing the plasticity of rub her which comprises milling unvulcanized rubber in the presence of a small amount oi a salt of a pseudo-urea, said salt being represented by the following general formula:

represents stearic acid. for a time sufficient to effect an increase in the plasticity oi the rubber over that which it would have if subjected to the same conditions in the absence of said salt.

3. A process of increasing the plasticity of rubber which comprises milling unvulcanized rubber in the presence of a small amount of Z-ethyl hexyl pseudo-urea stearate for a time sufficient to efiect an increase in the plasticity of the rubber over that which it would have if subjected to the same conditions in the absence of said salt.

4. A process of increasing the plasticity of rubber which comprises milling unvulcanized rub: her in the presence of a small amount of cyclohexyl pseudo-urea stearate for a time suflicient to efiect an increase in the plasticity of the rubher over that which it would have if subjected to the same conditions in the absence of said salt.

5. A process of increasing the plasticity of rubher which comprises milling unvulcanized rubber in the presence of a. small amount of lauryl pseudo urea stearate for a time sufllcient to efiect an increase in the plasticity of the rubber over that which it would have if subjected to the same conditions in the absence of said salt.

6. Unvulcanized rubber of increased plasticity comprising rubber having uniformly dispersed therein a small amount of pseudo-urea salt rep-= resented by the following general formula:

in which R is a, member of the class-consisting oi the cyclohexyl, benzyl and the alkyl radicals havine from about 4 to 18 carbon atoms and St represents stearic acid.

8. Unvulcanized rubber of increased plasticity comprising rubber milled with a small amount of Z-ethyl hexyl pseudo-urea stearate.

9. Unvulcanized rubber of increased plasticity comprising rubber milled with small amount of cyclohexyl pseudo-urea stearate.

10. Unvulcanized rubber of increased plasticity comprising rubber milled with a small amount of lauryl pseudo-urea stearate.

RUSSELL T. DEAN. 

